Issues Surrounding the Preservation of Digital Music Documents BRENT LEE RÉSUMÉ Les défis que pose la conservation des archives musicales ont été compli- qués au cours des dernières décennies par la création de documents sous forme numérique. Cette révolution numérique a affecté toutes les étapes de la création musicale traditionnelle, depuis l’ébauche et la notation des compositions jusqu’à l’enregistrement des performances. De plus, les nouvelles formes de musique unique- ment numériques impliquant la composition à l’aide d’algorythmes informatiques, d’environnements interactifs et de synthèse de son numérique ont amené la création de nouvelles variétés de documents numériques. Cet article décrit les différents types de documents qui sont produits aujourd’hui dans le cours du processus de création musicale et expose les défis que pose le passage du temps sur ces documents. Il s’arrête plus spécifiquement sur la capacité de les lire (comment savoir si nous pourrons récupérer correctement les documents numériques?), leur compréhension (comment pourrons-nous savoir ce que ces documents signifient exactement?), de même que sur l’adéquation entre leur représentation et leur authenticité (comment savoir que la fiabilité, l’identité et l’intégrité des documents n’ont pas été compromis d’une façon ou d’une autre?). Comprendre ces défis est crucial pour la conservation de notre culture musicale contemporaine. ABSTRACT The challenges of preserving musical archives have been complicated over the last few decades by the generation of documents in digital form. The digital revolution has affected all stages of traditional musical creation, from the sketching and notation of compositions to recordings of performances; also, new forms of uniquely digital music involving computer-aided algorithmic composition, interactive environments, and digital sound synthesis have created corresponding new varieties of digital documents. This study describes the types of documents currently generated in the process of making music and then articulates the challenges the passage of time poses for these documents, specifically: their readability (how do we know we will be able to retrieve the digital documents?) and intelligibility (how will we know what the documents mean?), as well as adequacy of representation and authenticity (how will we know that the reliability, identity, and integrity of the document has not been com- promised in some way?). Understanding these challenges is crucial for the preservation of our contemporary musical culture. Introduction Archives of traditional musical documents have enjoyed the same relative 194 Archivaria 50 stability as most other archives; the long shelf life and handling ease of paper have allowed for the preservation1 of documents over centuries. Still today, hitherto unknown manuscripts of even the most famous composers occasionally resurface in the archives of various individuals and institutions, such as the recent discovery of a string quartet movement by Beethoven in the possession of the family of John Ford, for whom the work was composed in 1817.2 The advent of recording technology in the twentieth century engendered a new type of musical document, the sound recording. The wide variety of processes and media developed for the recording of sound has proven to be problematic for archivists and librarians, both within public institutions and in the private sector. Record companies are only now developing strategies to cope with the imminent disintegration of their analogue master tapes, and the extent to which recorded material has already been compromised or completely lost is not yet known.3 The challenges of preserving musical archives have been complicated over the last few decades by the generation of documents in digital form. The digital revolution has affected all stages of traditional musical creation, from the sketching and notation of compositions to recordings of performances; also, new forms of uniquely digital music involving computer-aided algo- rithmic composition, interactive environments, and digital sound synthesis have created corresponding new varieties of digital documents. This study describes the types of documents currently generated in the process of making music and then articulates the challenges the passage of time poses for these documents, specifically: their readability (how do we know we will be able to retrieve the digital documents?), intelligibility (how will we know what the documents mean?), as well as adequacy of representation and authenticity (how will we know that the reliability, integrity, and identity of the document have not been compromised in some way?). Understanding these challenges is crucial for the preservation of our contemporary musical culture. Data Formats Data formats designed to represent notated music (scores and sketches), audio recordings of musical performances, and other miscellaneous aspects of musical composition have proliferated over the last several decades. While a 1 I am using the term “to preserve” in a broad sense, i.e., to permanently maintain. 2 Abigail Frymann, “New Beethoven Piece Discovered in Cornwall,” Gramophone 77, no. 922 (December 1999), p. 23. 3 For a further discussion of efforts on the part of the recording industry to preserve their archives, see Bill Holland, “A Management/Preservation Scorecard,” Billboard – The Interna- tional Newsweekly of Music, Video, and Home Entertainment 111, no. 45 (6 November 1999), p. 92. Issues Surrounding the Preservation of Digital Music Documents 195 few data formats have (at least for a period of time) been adopted as industry standards, musical archival documents have been generated in a bewildering array of formats. Their diversity arises from differences among the various computers used to create the music, among the particular operating systems (and versions of these systems) that reside on computers, among the various music software packages for these systems, and among the variety of file interchange formats developed to cope with these differences. The digital representation of music can be broken down into three broad categories based on the type of information represented. The first category includes file formats that represent actual sound (digital recordings), while the second includes formats that represent notated music (notation files). A third category includes formats that represent neither notated nor recorded music, but serve to control computer operations that could then generate notation or sound. Digital Recording (Audio) Formats Digital audio files have one thing in common: they all contain a stream of numbers that represent changes in the amplitude of sound pressure over time. When sound is recorded digitally, a measuring device records the amplitude of the sound thousands of times each second. Each of these measurements is called a sample. The frequency at which samples are measured is called the sampling rate, and is described in samples/second. Thus a sampling rate of 44.1KHz (the rate used for CDs) means that the sound amplitude was mea- sured and recorded 44,100 times each second. The higher the sample rate, the better the sound quality, as it gives a more detailed representation of the sound. For example, imagine a curve being represented by the series of numbers 1, 2, 5, 9, 11, 13, 16, 13, 10, 8, 6, 4, 3, 2, 1. If one plotted these numbers on graph paper and connected the dots, one could reconstruct the curve. One could represent the same curve by a series comprising every second number of the original series – 1, 5, 11, 16, 10, 6, 3, 1 – but this reconstruction would not be as detailed as the one with more numbers. Sampling rate is only one of several variable elements that affect the structure of an audio file. Others, which will be explained below, include the precision of the measurement or sample size, the number of channels, the encoding algorithm, the type of compression used (if any), and possibly commands and/or information useful to the operating system for which the file format was developed. The sample size used in the recording of a digital sound document also affects the recording’s fidelity to the original sound; the larger the sample size, the more precise the measurement. The most common sample sizes are 8-bit (a scale of 0 to 255) and 16-bit (a scale of 0 to 65535), though 24-bit (a scale of 0 to 16777215) is becoming an industry standard for professional audio. 196 Archivaria 50 Most of the other variable elements mentioned above affect the file format (the way the information is stored) more than the quality of sound. For example, many audio file formats allow for a variable number of channels. A file could be monophonic (one channel), stereophonic (two channels), or any number of discrete channels. The samples themselves can be encoded in different ways; most encoding schemes are linear, but some are logarithmic. In some encoding schemes, the samples are interpreted as signed or unsigned integers; an 8-bit recording may represent values from zero to 255 or –128 to +127. In addition, some file formats (like MP3) use a compression scheme to greatly reduce the file size. Consider again the series of numbers used in the sampling example: 1, 2, 5, 9, 11, 13, 16, 13, 10, 8, 6, 4, 3, 2, 1. This same series could be encoded with numbers which represent the change from one measurement to the next: +1, +3, +4, +2, +3, –3, –3, –2, –2, –2, –1, –1, –1. In this second set, the numbers are much smaller, and can thus be stored in a smaller file. Lastly, audio files generally contain commands and informa- tion specific to the systems to which they belong. Such files are only readable by certain computer systems. The variety of operating systems used to create music accounts for the wide array of file formats developed for use within these systems, including AU (Macintosh), WAV (Windows), SND (Amiga), and AVR (Atari). The AIFF (Audio Interchange File Format) was developed by Apple in the late 1980s in accordance to the EA IFF 85 standard developed by Electronic Arts; due to its flexibility and non-proprietary nature, AIFF has since become a widely used format for audio files.